Method and apparatus for shredding foam

ABSTRACT

Foam, such as foamed beads, are shredded into irregularly shaped particles having random and irregular exterior surfaces, tears and ragged edges to rupture and open a substantial number of the foam cells. The foam beads are passed between relatively moving, opposing shredding surfaces including toothlike serrations. Oversize shredded particles are separated on a screen from which they are recycled for reshredding and size reduction. The apparatus also includes structure for feeding the foam beads to the shredding surfaces and collecting the shredded and screened particles for removal from the apparatus.

Milled Males palatial [72] inventor lirhy 11. Leach 2094 Emerson, Nana,(21211111. 514351? 21 1 Appl. No. Mama '[22] Filed 1111113 215, 1969[45] Patented Dec. 14, 19711 [54] ll/lllE'lllllIUlD AND AMPAWATIUS lFQlRSllllllmlDlDllNG ll OAll/ll 10 Claims, 41 Drawing ll lgs.

[52] US. Cl 241/3,

241/18, 241/24, 241/49, 241/60, 241/73 [51] 1m. (31 "Mme 113/22, lBOZc18/44 [50] Field 011 Search 241/3, 18, 19, 49, 73,190, 236, 60

[56] Weller-anew Clted UNITED STATES PATENTS 2,461,089 2/1949 Smidth241/3 2,903,193 9/1959 Anderson 241/73 3,241,776 3/1966 She1don.. 241/73X 3,453,221 7/1969 Richart 241/3 X Primary Examiner-Donald G. KellyAttorney-Townsend and Townsend ABSTRACT: Foam, such as foamed beads, areshredded into irregularly shaped particles having random and irregularexterior surfaces, tears and ragged edges to rupture and open asubstantial number of the foam cells. The foam beads are passed betweenrelatively moving, opposing shredding surfaces including toothlikeserrations. Oversize shredded particles are separated on a screen fromwhich they are recycled for reshredding and size reduction. Theapparatus also includes structure for feeding the foam beads to theshredding surfaces and collecting the shredded and screened particlesfor removal from the apparatus.

mmwnmmm SHEET 1 OF 2 memn F I G I .INVENTOIL IRBY H.LEACH BY ATTORNEYSmmmamm SHEET 2 [IF 2 Ill/I FIG-3 INVENTOR.

lRBY H. LEACH FIG-4 ATTORNEYS METHOD AND APPARATUS FOR SIIMEDDING FOAMRELATED APPLICATIONS This patent application is related to thecopending, commonly owned patent applications bearing Ser. No. 844,344filed July 25, 1969, for METHOD FOR PRODUCING LOW- DENSITY FOLYSTYITENEFOAM, and Ser. No. 844,895 filed July 25, 1969, for GRANULAR FOIRMATIONSIN- CLUDING OIPEN CELL POLYSTYJRENE PARTICLES.

BACKGROUND OF THE INVENTION There is a wide need for shredded foammaterials as a filler, a base material or for providing means to reducethe density of heavy, high-density materials. Particulars of the latterapplication are contained in the second patent application referred toabove.

Low-density, low-cost foam is most commonly available in the form offoamed or expanded polystyrene beads. For example, see the first listedpatent application referred to above which enables the production ofpolystyrene foam having densities of as low as 0.2 pounds per cubic footon an economical basis.

In the prior art, the reduction of the foam into small particle sizesgenerally provided for the cutting or chopping of the foam. This yieldsclean cut particles having an appealing appearance and has the furtheradvantage that virtually any particle size can be obtained. However, thecut surface areas on the finished particles are relatively small.Consequently, the number of foam cells opened by the cuts is relativelysmall since the surface areas created by the cuts intersect only a fewfoam cells.

In many applications it is desirable to maximize or at least have asubstantial number of open cells for the subsequent processing of thefoam particles. The nature of the size reduction of the foam inaccordance with prior art methods and apparatus runs counter to thatobjective since the surface area of a foamed particle of a given sizerequires a maximization of such surfaces, as by giving them an irregularand uneven configuration, instead of a planar configuration obtained inthe prior art.

SUMMARY OF THE INVENTION The present invention provides a method andapparatus to form small size foam particles having a substantial numberof open cells. The particles are shredded by passing them between tworelatively moving tearing surfaces defined by tooth-shaped serrations.The particles have randomly disposed, nonplanar exterior surfaces,including tears extending from the surfaces towards the interior of theparticles and serrated ridges to maximize the areas of the varioussurfaces and to thereby intersect and open a substantial number oftheretofore closed foam cells.

The apparatus of the present invention comprises a housing mounting onits interior a pair of spaced-apart parallel shredding rolls having theabove-mentioned tear surfaces. The rolls are rotated so that thesurfaces move at differing speeds. A screen is placed beneath the rollsfor separating excessively large particles. Particles passing the screenare collected and introduced into an airstream for removal from thehousing. The screen is so shaped that excessively large particles areplaced closely adjacent the periphery of the shredding rolls whereby therotational movement of the rolls, through physical contact and/or anair-stream induced by the rotating rolls transports the oversizeparticles for recycling and further size reduction. The apparatus isalso provided with chute means to introduce the foam, preferably in theform of foam beads, to the shredding rolls.

The apparatus permits a high volume production of small size shreddedfoam particles which are ideally suited for the subsequent use of theparticles in applications requiring open cells. In a preferredembodiment of the invention the shredding rolls are defined by aplurality of large and small diameter, axially spaced shredding discswhich are so arranged that the large diameter discs interlace and facesmall diameter discs on the opposite roll. The housing is so positionedthat the axes of the shredding rolls lie in a substantially horizontalplane and the rolls are rotated in opposing directions so that particlesdeposited on top of the rolls are drawn into the gap between the rolls.The particle sizes can be varied by increasing or decreasing the gapbetween the rolls and by selecting a screen of the proper mesh size. Toassure removal of excessively large particles from the top surface ofthe screen the spacing between the latter and the periphery of the rollsis controlled as more fully set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic frontelevational view, with parts broken away, of a shredding apparatus forthe manufacture of shredded, open cell foam particles;

FIG. 2 is an enlarged elevational view, in section, and is taken on line2-2 of FIG. ll;

FIG. 3 is a fragmentary, enlarged plan view, in section, of theintermeshing tearing surfaces of the apparatus illustrated in FIG. I andis taken on line 3-3 of FIG. ll; and

FIG. I is a plan view of a foamed particle shredded in accordance withthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 11 through3, a shredding machine h comprises an upright housing If) defined by abase section 112 and a cover 114 demountably secured to the top of thebase section. A pair of intermeshing shredder rolls If are rotatablymounted and disposed interiorly of the housing and actuated by drivemeans iii. A chute 20 is secured to cover Id and positionedsubstantially vertically above the median between the two shredderrolls. The base section includes a collector funnel 22 beneath the rollsthat terminates in a passageway 24 leading into a suction side 26 of anair blower 28. The impeller of the blower is also driven by drive meansId. The pressure side of the blower is connected to a conduit 30terminating at the exterior ofhousing It) in a connecting flange 32.

In operation particles to be shredded enter through chute 20, areshredded or torn by the coaction of the shredder rolls It, are collectedby funnel 22 and fed to the suction side 2s of blower 22 for transportto a point of use as more fully described hereinafter.

The shredder rolls are preferably of identical construction and eachcomprises a shaft 34 rotatably mounted in journal bearings 36 secured tothe exterior of the housing If) in a conventional manner. One side ofthe shaft includes an annular ring 3% while another side of the shaftincludes a threaded portion 40. Both the ring and the threaded portionare inward of the shaft extremities which extend through the journalbearings. A multiplicity of large and small diameter, circulardisc-shaped tear plates 42 and 44, respectively, are alternatinglyspaced over the length of shaft 34 between ring 38 and threaded portion40. The tear plates are spaced apart by spacers 456 a distance aboutequal to or slightly greater than the thickness of the tear plates. Theperiphery of the tear plates includes regularly spaced, transverse andgenerally tooth-shaped serrations 4b which have a depth of between aboutone sixty-fourth to about three-sixteenths of an inch, the preferreddepth range being between about one-sixteenth to about one-eighth of aninch for the shredding of foamed polystyrene beads as more fullydescribed hereinafter.

Referring particularly to FIGS. l and 3, the actual spacing betweenshafts 34 of the shredder rolls is slightly greater than the combinedradii of the small and the large diameter tear plates 42 and 44 out isless than the combined distance of the radii of two large tear plates 42so that the tear plates of the two shredder rolls overlap (as best shownin FIGS. 1 and 3) and the tear plates interlace. There remains a narrowgap 50 between the tear surfaces 52 of opposing tear plates of the twoshredder rolls. The magnitude of the gap is a function of the desiredsize of the shredded particles. For the shredding of foamed polystyrenebeads having a density of between about 0.2 and about 0.5 pounds percubic foot, an expanded head size of between about one-fourth to aboutthree-fourths inch diameter, and a desired shredded maximum particlesize of about three-sixteenths of an inch, gap 50 has a width of aboutone thirty-second inch.

Referring again to FIGS. I through 3, a screen 54 is placed beneathshredder rolls l6 and is secured to sidewalls of housing base section 12in a conventional manner as with threaded bolts. Generally, the screenhas a double crescent shape (as shown in FIG. 1) and is defined by acenter ridge 56, a first screen section 58 between the center ridge anda point 60 about vertically below the shaft 34, and a second screensection 62 extending from point 60 to housing base section 12.

The first screen section has a circular configuration with the center ofthe circle being the axis of the corresponding shredder shaft 34 so thatthe screen section is parallel to the tear surfaces of the tear plates42, 44. The radius of the first screen section is such that the spacingbetween the section and the tear surfaces is in the range not exceedingthe maximum desired average dimension of the shredded particles plusabout one-sixteenth inch. In the above example in which polystyrene foamparticles are shredded to a maximum dimension of about three-sixteenthinch the spacing between the tear plate tear surfaces 52 and the firstscreen section 58, in a radial direction, is about one-sixteenth inch.

The second screen section is eccentric with the tear plates and thespacing, in a radial direction, between the tear surfaces and the secondscreen section increases gradually and continuously from adjacent point60 to the end of the second screen section. The maximum spacing betweenthe tear surfaces and the end of the second section is not critical.

The screen as such may be constructed of a variety of materials and hasmesh or screen openings which permit the passage of the desired particlesizes and prevent particles having excess dimensions from passing thescreen. It is presently preferred to construct the screen of stamped-outsheet metal which lends itself readily to forming to give it the desiredshape. If convenient, other materials, such as wire mesh, can beemployed.

The dimensioning and shaping of the screen 54 is important to preventshredded particles from clogging the space between the tear surfaces andthe screen which can render the shredder inoperable. Contrary to theexpected effect, an increase in the spacing between the tear surfacesand the screen beyond the above-stated range leads to an increasedtendency of clogging. The exact dimensionality of the spacing betweenthe tear surfaces and the first screen sections 58 is further a functionof the material being shredded and may require periodic adjustments ofthe spacing.

To enable the ready transport of oversized shredded particles away frombeneath the shredder rolls the second screen sections 62 open up.Oversize shredded particles incapable of passing through the screen arethereby recirculated by the shredder rolls (as described below) into theupper space of housing cover 14 for reshredding. Waste of oversizeparticles is prevented and the recirculation and reshredding isaccomplished without additional feeding mechanisms and the like.

Referring to FIGS. 1 and 3, drive means 18 is schematically illustratedand comprises a relatively small diameter pulley 64 mounted to one ofthe extremities of the left-hand shredder shaft 34 (as seen in FIG. I),a relatively large diameter pulley 66 mounted to the extremity of theright-hand shredder shaft and a pulley 68 mounted to the extremity ofair blower shaft 29 on the side of housing so that it is aligned withpulley 64. A pair of axially spaced idler pulleys 70, 7i areinterconnected and mounted on the exterior of housing 10. Each idlerpulley is aligned with one of the shredder pulleys 64, 66.

A conventional electric motor 72 is mounted to a support plate 74 andincludes a pulley 76 over which a belt 78 is looped. Belt 78 is furtherlooped over one of the idler pulleys 70, blower pulleys 68 and theleft-hand, small diameter shredder roll pulley 64. A second belt 80 islooped over the second idler pulley 71 and the right-hand, largediameter shredder roll pulley 66. The electric motor is hooked up sothat its pulley rotates in a clockwise direction whereby the left-handshredder roll also rotates in a clockwise direction and the right-handshredder roll (as seen in FIG. I) rotates in a counterclockwisedirection. Materials being shredded and entering the shredding machine 8through chute 20 are thereby drawn into gap 50 between tear surfaces 52.

Aside from rotating in opposing directions the tear surfaces 52 move atdifferent relative speeds. Consequently pulleys 64, 66, 70 and 71 arearranged so that one of the shredder rolls, say the left-hand roll,rotates at a higher r.p.m. than the lefthand roll. In a presentlypreferred embodiment of the invention the pulleys are arranged so thatthe relative speed differential between the tear surfaces, and thereforethe r.p.m. differential between rolls, is between about I: l .5 to about1:6, with the preferred speed differential being about 1:4.

Turning now to the operation of the shredding apparatus, with particularreference to the shredding of the above-mentioned foamed polystyrenebeads, the beads enter through chute 20 and fall gravitationally intospace 82 between and above the two shredder rolls l6. Serrations 48 oftear plates 42, 44 grasp the beads and pull them downwardly. Due to thespeed difi'ercntial of the tear surfaces 52 the beads are shredded intosmall particles 84 (shown in FIG. 5) in gap 50 between the tearsurfaces. The movement of the tear surfaces transports the particlesdownwardly until they contact screen 54. Those particles which aresmaller than the screen openings fall through the openings and henceunto collector funnel 22. The suction at suction side 26 of air blower28 enhances the passage of those particles through the screen and theirmovement towards the blower. Shredded particles which are large, i.e.which have a dimension greater than the maximum dimension of the screenopenings, are prevented from passing the screen. They remain on theupper surface of the screen and are transported in the direction ofrotation of the shredder rolls 16 towards the second screen sections 62.This removal of the excessively large particles is aided by directcontact between serrations 48 and such particles and by air movements orcurrents in the vicinity of the tear plate peripheries caused by therelatively highspeed of the rolls. Thus, the oversize particles are inefi'ect blown into the upper portion of housing cover 14 and into space82 from where they are recycled through the shredder rolls forreshredding and size reduction.

Referring briefly to FIG. 4, a shredded particle 84 is illustrated. Ithas a generally elongate configuration although the particle can alsohave a more compact shape since all particle dimensions, shapes, etc.are purely random. The particle includes a randomly shaped, nonplanarand uneven exterior surface 88, randomly disposed, sized and formedtears extending from the exterior surface towards the center of theparticle and ragged or serrated ridges or edges 92. The total exteriorsurface area of the particle is therefore defined by the exteriorsurfaces, the surfaces defined by the tears and those defined by theridges. These surfaces intersect large numbers of for merly closed foamcells 94 which therefore become open cells.

I claim:

1. A method of forming low-density open cell foamed particles comprisingthe steps of: expanding polystyrene beads into low-density, foamedpolystyrene beads, and shredding the expanded beads between opposing,relatively moving tearing surfaces having tooth-shaped serrations andengaging the beads to shred the beads into particles having nonplanar,randomly distributed, uneven exterior surfaces, randomly distributedragged ridge members and randomly distributed tears extending from thesurfaces towards the interior of the particles to thereby open particlecells disposed at the surfaces, ridge members and tears to theatmosphere.

2. A method according to claim I wherein the tear surfaces have asubstantially circular configuration, wherein opposing pairs of tearsurfaces rotate in opposing directions at different rates of rotation,and wherein the method comprises the further steps of screening shreddedparticles and recirculating oversized particles rejected during thescreening step.

3. A method according to claim 2 wherein the step of recycling comprisesthe steps of positioning the rejected particles on a surfacesubstantially concentric with and spaced from the periphery of thetearing surfaces, rotating the tearing surfaces at a sufficient speed tocause removal of the particles in the direction of rotation of thetearing surfaces, and guiding the removed particles towards the opposingtearing surfaces for reahredding and size reduction.

41. A method according to claim 11 including the step of collectingparticles passing through the screen, and placing the collectedparticles into an airstream for transportation of the particles towardsa point of use.

d. A method for forming open cell foamed polystyrene particles fromclosed cell foamed polystyrene heads, the method comprising the stepsof: rotating a pair of opposing rollers having substantiallycylindrical, serrated surfaces in opposing directions, placing the beadsonto the rollers so that the serrated surfaces pull the beads towards agap between the surfaces, moving the serrated surfaces at differingspeeds to thereby shred the beads into randomly shaped foamed particleshaving a substantial number of open cells, separating excessively largeparticles from the remainder of particles, recirculating the largeparticles for additional shredding and size reduction, and collectingthe remaining particles.

if. A method according to claim 5 wherein the speed differential betweenthe serrated surfaces is between about l:l.5 to about 1:6.

7. A method according to claim 5 wherein the step of recycling comprisesthe steps of positioning the oversize particles adjacent the cylindricalsurfaces and substantially concentrically therewith and sweeping theoversize particles in the direction of rotation of the cylindricalsurfaces through physical contact between the surfaces and the particlesand creation of an airstream adjacent the surfaces, and directing theparticles baclt into the space between the surfaces.

h. Apparatus for shredding closed cell foam into foam particles havingopen cells, the apparatus comprising: a housing, a pair of parallel,spaced-apart shredding rolls defining a gap therebetween, each rollhaving a substantially circular periphery and a plurality ofsawtoothlike serrations on the periphery, drive means rotating the rollsin opposing directions to cause a shredding of the foam passing into thegap, each roll comprising a plurality of axially spaced large and smalldiameter circular discs having a serrated periphery and wherein therollers are positioned so that the large diameter discs of the rollsinterlace and are opposite small diameter discs of the other roll, meansfor guiding the foam into the gap, and means for collecting shreddedfoam particles and removing them from the housing.

9. Apparatus for shredding closed cell foam into foam particles havingopen cells, the apparatus comprising: a housing, spaced-apart foamshredding rolls defining a gap therebetween, drive means for rotatingthe rolls in opposing directions for shredding foam passing through thegap, and a screen mounted to the housing and positioned downstream ofthe gap for preventing excessively large particles from passing throughthe screen and for returning the excessively large particles to anupstream end of the gap for recirculation and further size reduction,the screen having first sections extending from a screen centersubstantially aligned with the gap to a point intermediate the centerpoint and a corresponding end of the screen in the direction of rotationof the adjacent roll, the first sections being substantially concentricwith the ad jacent roll periphery and spaced therefrom, and secondsections between the intermediate point and the adjacent screen end, thesecond sections being eccentric with respect to the roll peripheries andarranged so that the distance between each roll periphery and theadjacent second screen section increases in the direction of rotation ofthe rolls.

10. Apparatus for shredding foam beads into small size,

generally ragged foamed particles having open cells, the apparatuscomprising: a closed housing, means defining a pair of movable,spaced-apart shredding surfaces having toothshaped protrusions arrangedtransversely to the direction of movement of the surfaces, a screenplaced beneath the surfaces and comprising first and second screenhalves meeting at a screen center beneath a gap between the surfaces,each screen half further having a first section extending substantiallyparallel to an adjacent shredding surface away from the screen center,and a second section contiguous with the first section and extendingnonparallel with respect to the adjacent shredding surface, at least oneof each second section and interior portions of the housing beingarranged for guiding shredded particles too large to pass through thescreen back to an upstream end of the gap for recirculation of suchparticles, collection means disposed beneath the screen for collectingthe particles and removing them from. the housing, and drive means formoving the shredding surfaces with respect to each other.

W l t l '3'

2. A method according to claim 1 wherein the tear surfaces have asubstantially circular configuration, wherein opposing pairs of tearsurfaces rotate in opposing directions at different rates of rotation,and wherein the method comprises the further steps of screening shreddedparticles and recirculating oversized particles rejected during thescreening step.
 3. A method according to claim 2 wherein the step ofrecycling comprises the steps of positioning the rejected particles on asurface substantially concentric with and spaced from the periphery ofthe tearing surfaces, rotating the tearing surfaces at a sufficientspeed to cause removal of the particles in the direction of rotation ofthe tearing surfaces, and guiding the removed particles towards theopposing tearing surfaces for reshredding and size reduction.
 4. Amethod according to claim 1 including the step of collecting particlespassing through the screen, and placing the collected particles into anairstream for transportation of the particles towards a point of use. 5.A method for forming open cell foamed polystyrene particles from closedcell foamed polystyrene beads, the method comprising the steps of:rotating a pair of opposing rollers having substantially cylindrical,serrated surfaces in opposing directions, placing the beads onto therollers so that the serrated surfaces pull the beads towards a gapbetween the surfaces, moving the serrated surfaces at differing speedsto thereby shred the beads into randomly shaped foamed particles havinga substantial number of open cells, separating excessively largeparticles from the remainder of particles, recirculating the largeparticles for additional shredding and size reduction, and collectingthe remaining particles.
 6. A method according to claim 5 wherein thespeed differential between the serrated surfaces is between about 1:1.5to about 1:
 6. 7. A method according to claim 5 wherein the step ofrecycling comprises the steps of positioning the oversize particlesadjacent the cylindrical surfaces and substantially concentricallytherewith and sweeping the oversize particles in the direction ofrotation of the cylindrical surfaces through physical contact betweenthe surfaces and the particles and creation of an airstream adjacent thesurfaces, and directing the particles back into the space between thesurfaces.
 8. Apparatus for shredding closed cell foam into foamparticles having open cells, the apparatus comprising: a housing, a Pairof parallel, spaced-apart shredding rolls defining a gap therebetween,each roll having a substantially circular periphery and a plurality ofsawtoothlike serrations on the periphery, drive means rotating the rollsin opposing directions to cause a shredding of the foam passing into thegap, each roll comprising a plurality of axially spaced large and smalldiameter circular discs having a serrated periphery and wherein therollers are positioned so that the large diameter discs of the rollsinterlace and are opposite small diameter discs of the other roll, meansfor guiding the foam into the gap, and means for collecting shreddedfoam particles and removing them from the housing.
 9. Apparatus forshredding closed cell foam into foam particles having open cells, theapparatus comprising: a housing, spaced-apart foam shredding rollsdefining a gap therebetween, drive means for rotating the rolls inopposing directions for shredding foam passing through the gap, and ascreen mounted to the housing and positioned downstream of the gap forpreventing excessively large particles from passing through the screenand for returning the excessively large particles to an upstream end ofthe gap for recirculation and further size reduction, the screen havingfirst sections extending from a screen center substantially aligned withthe gap to a point intermediate the center point and a corresponding endof the screen in the direction of rotation of the adjacent roll, thefirst sections being substantially concentric with the adjacent rollperiphery and spaced therefrom, and second sections between theintermediate point and the adjacent screen end, the second sectionsbeing eccentric with respect to the roll peripheries and arranged sothat the distance between each roll periphery and the adjacent secondscreen section increases in the direction of rotation of the rolls. 10.Apparatus for shredding foam beads into small size, generally raggedfoamed particles having open cells, the apparatus comprising: a closedhousing, means defining a pair of movable, spaced-apart shreddingsurfaces having tooth-shaped protrusions arranged transversely to thedirection of movement of the surfaces, a screen placed beneath thesurfaces and comprising first and second screen halves meeting at ascreen center beneath a gap between the surfaces, each screen halffurther having a first section extending substantially parallel to anadjacent shredding surface away from the screen center, and a secondsection contiguous with the first section and extending nonparallel withrespect to the adjacent shredding surface, at least one of each secondsection and interior portions of the housing being arranged for guidingshredded particles too large to pass through the screen back to anupstream end of the gap for recirculation of such particles, collectionmeans disposed beneath the screen for collecting the particles andremoving them from the housing, and drive means for moving the shreddingsurfaces with respect to each other.